Thin film transistor (TFT), such as In—Ga—Zn—O (IGZO) TFT, is a basic circuit component which can be widely applied in a variety of electronic systems, and has many advantages, such as high electron mobility, low temperature manufacturing process, high stability, transparency, and so on. However, in the prior process for manufacturing a thin film transistor, due to the increased overlaps between the gate and the source and drain, the gate-source parasitic capacitance is high, so that the overall performance of the thin film transistor is poor. Further, there is a high alignment requirement on the mask plate in the prior process for manufacturing a thin film transistor, with a low yield and high costs. Also there is a high alignment precision requirement on the mask plate in the four-mask TFT process which use the gray tone masks, thus also affecting the yield and the costs.